Round Earth......I have never heard of or met people who believe in the Flat Earth idea. I understand that belief in a round or spherical Earth goes back to Plato, and maybe to others. Sailors were said to have been able to determine the spherical nature of the earth by seeing the curve in the horizon on the ocean.
I am not sure that calling people "stupid" is a valued method of discourse, no matter what country you live in. Arrogance or pride are things which God hates. Find it in the Bible!! Supposing that someone who disagrees with you is thus "stupid" and not worthy of God's time is somewhat deficient. The Nazis had death camps with sections for "useless eaters," the majority of which had IQs lacking in the level of sophistication you seem to seek. And you and I might also be so classified by the Nazis or some similar group for one reason or another.
The fact is that you and I may have higher IQs than some but not higher than all. We certainly do not know more than God, who created all of us to have friendship with Him and gave us different gifts ....even to the "low IQ" folks who distress you.